Solid Homogeneous Mixture Of Polyvinylacetate and Vinylacetate-Vinyl Laurate Copolymer Prepared By Sequential Solution Polymerization

ABSTRACT

The invention provides a chewing gum base containing a homogeneous composition in solid form comprising 
     a) from 50 to 90% by weight of polyvinyl acetate and 
     b) from 10 to 50% by weight of vinyl acetate-vinyl laurate copolymer, the weight percentage based on the total weight of the composition.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. application Ser. No.12/057,437,filed Mar. 28, 2008, which, in turn, claims the benefit of U.S.provisional Application No. 60/909,497, filed Apr. 2, 2007. Thedisclosure(s) of which are incorporated in their entirety by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to compositions composed of polyvinyl acetate andvinyl acetate-vinyl laurate copolymer, to processes for their productionand to their use in chewing gum base.

2. Background Art

Typically, chewing gum formulations are composed of a water-insolublechewing gum base and a water-soluble fraction, the latter comprisingsweeteners and flavorings which are leached out by the saliva duringchewing.

In general, in the production of chewing gum base, in addition to solidelastomers, for example polyisobutylene, isobutylene/isoprene copolymersand/or butadiene/styrene copolymers, a vinyl acetate homopolymer is usedas a polymer resin. Suitable elastomer solvents are, for example,polyterpenes or glyceryl esters of rosin or partially hydrogenatedrosin. The plasticizers used are frequently hydrogenated vegetable oils,cocoa butter, paraffin waxes, natural waxes and polyethylene. Additionalplasticization is achieved by the use of triacetin, and/or emulsifierssuch as glyceryl monostearate, acetylated monoglycerides of naturalfatty acids and/or lecithin.

The chewing gum bases can be produced in one or more stages. Typically,in a batchwise process, mixers or double-Z kneaders with high shearforce are used for this purpose. Alternatively, EP 0763328 describescontinuous processes in which the chewing gum base is produced in anextruder.

U.S. Pat. No. 4,968,511 recommends using, as the chewing gum base, oneor more polymers such as homopolymers of vinyl esters of carboxylicacids having from 3 to 10 carbon atoms, copolymers of two differentvinyl esters, copolymers of vinyl ester and ethylene, and theterpolymers of vinyl alcohol, vinyl ester and ethylene. To produce thegum base, the individual constituents of the formulation, such aspolymer resin, elastomer, filler and emulsifier, are meteredsuccessively into a preheated mixer.

U.S. Pat. No. 5,173,317 discloses the use of vinyl acetate-vinyl lauratecopolymers instead of polyvinyl acetate as the gum base. Owing to theelastomeric properties of vinyl acetate-vinyl laurate copolymers, it ispossible to dispense with the use of further elastomers in theformulation. Here too, the individual constituents of the formulationare metered successively into a preheated mixer and mixed in the melt.

A disadvantage in the case of use of vinyl acetate-vinyl lauratecopolymers is that they are obtained as tough, elastic blocks whichcannot be used directly in the customary processes for producing chewinggum mixtures in batch kneaders or extruders. The blocks have to becomminuted beforehand, which is possible only with a high level of costand inconvenience owing to the tough, elastic material, for example byfreezing the material and subsequent comminution. A further means ofconverting the vinyl acetate-vinyl laurate copolymers to aready-to-process form is to melt them and to meter them into the kneaderor extruder as a melt.

SUMMARY OF THE INVENTION

It was therefore an object of the invention to modify the vinylacetate-vinyl laurate copolymers in such a way that they are provided ina form which enables metered addition in the course of processing togive chewing gum base without the operator having to carry out thecostly and inconvenient process steps mentioned, and with which thepolymer resin and/or elastomer content of conventional formulations canbe replaced completely or partly. These and other objects are met byutilizing, instead of separate vinyl acetate and vinyl acetate-vinyllaurate copolymers, a solid, homogeneous solid blend of vinyl acetatecopolymer and vinyl acetate-vinyl laurate copolymer.

The invention provides homogeneous compounds in solid form comprising

a) from 50 to 90% by weight of polyvinyl acetate andb) from 10 to 50% by weight of vinyl acetate-vinyl laurate copolymer,based in each case on the total weight of the compound.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The composition is in a homogeneous form, i.e. in the form of particleswhich comprise both fractions of polyvinyl acetate a) and fractions ofvinyl acetate-vinyl laurate copolymer b). The composition present inparticulate, room temperature solid form. In general, the particle sizeis from 1 to 20 mm. Preference is given to granules, pastilles andpellets. In a further preferred embodiment, the particles are powderedwith antiblocking agent, for example talc or fumed silica. Theantiblocking agent content is preferably up to 5% by weight, based onthe weight of the particles.

The compositions contain preferably from 60 to 80% by weight ofpolyvinyl acetate and from 20 to 40% by weight of vinyl acetate-vinyllaurate copolymer, based in each case on the total weight of thecomposition, and where the figures in % by weight each add up to 100% byweight. Particular preference is given to compositions comprising from65 to 75% by weight of polyvinyl acetate and from 25 to 35% by weight ofvinyl acetate-vinyl laurate copolymer.

The polyvinyl acetates are generally polyvinyl acetate homopolymers.When the polyvinyl acetate is prepared in the presence of the vinylacetate-vinyl laurate copolymer, it is possible for small fractions ofvinyl laurate to be copolymerized, generally less than 10% by weight,preferably up to 5% by weight, based on the total weight of thecopolymer. Preference is given to polyvinyl acetates having aweight-average molecular weight Mw of from 10,000 to 100,000, morepreferably from 15,000 to 55,000.

The vinyl acetate-vinyl laurate copolymer contains preferably from 50 to90% by weight of vinyl acetate units and from 10 to 50% by weight ofvinyl laurate units, more preferably from 60 to 80% by weight of vinylacetate units and from 20 to 40% by weight of vinyl laurate units. Theweight-average molecular weight Mw of the vinyl acetate-vinyl lauratecopolymer is preferably from 100 000 to 600 000. The weight-averagemolecular weight Mw was determined in each case by means of sizeexclusion chromatography, SEC, in THF with a polystyrene standard.

The component a) may also be a mixture of polyvinyl acetates ofdifferent molecular weight. Equally, the component b) may be a pluralityof vinyl acetate-vinyl laurate copolymers with different copolymercomposition and/or different molecular weights.

The compounds can be produced by mixing the melts of one or morepolyvinyl acetates a) and one or more vinyl acetate-vinyl lauratecopolymers b).

Polyvinyl acetates a) suitable for this purpose and suitable vinylacetate-vinyl laurate copolymers b) are commercially available, forexample Vinnapas® solid resins from Wacker Chemie AG. The polyvinylacetate component a) and the vinyl acetate-vinyl laurate copolymercomponent b) can also be prepared in a known manner by means of bulk orsolution polymerization. A suitable process is described, for example,in EP 1352914. To this end, the appropriate monomers are polymerized inthe presence of initiators, such as peroxide or azo initiators,optionally in a usually alcoholic solvent and optionally in the presenceof regulators, at a temperature of generally from 40° C. to 140° C., andany solvent and regulator and residual monomer is distilled off.

To prepare the compounds by means of mixing of the melts of component a)and b), the polyvinyl acetate a) and the vinyl acetate-vinyl lauratecopolymer b) can be metered as solids into a preferably preheatedstirred tank, kneader or extruder, and are preferably melted and mixedat a temperature of from 80° C. to 140° C. The procedure is preferablysuch that the polymer with the lower melt viscosity, usually thecopolymer b), is initially charged at processing temperature and thenthe other component, usually the polyvinyl acetate a), is added. Themixing time is generally from 5 to 90 minutes, according to which mixingunit is selected.

The compositions thus obtainable are mechanically comminuted aftercooling, for example in a mill or a crusher. The compounds can also becooled as a melt on a cooling belt in the form of strips, slabs ordrops. A further alternative consists in processing the melt to pelletsby means of underwater granulation, in which case preference is given toa particle size of from 1 mm to 20 mm for the pellets, and particularpreference is given to a particle size of from 3 mm to 10 mm. Solidcompositions are thus obtainable in particulate, dosable andfree-flowing form.

In a preferred embodiment, the compositions are produced by means ofsolution polymerization. To this end, the comonomers of component b),vinyl acetate and vinyl laurate, are initially charged in the desiredquantitative ratio, and the polymerization is carried out at atemperature of from 40° C. to 120° C. The initiator can be initiallycharged completely or partly and the remainder can be metered in. Thesolvent can be initially charged completely or partly and the remaindercan be metered in. Suitable solvents are aldehydes, ketones, preferablyalkanols such as methanol, ethanol, propanol, and isopropanol. When themonomers of component b) have copolymerized to an extent of from 60 to100% by weight, preferably from 60 to 90% by weight, vinyl acetate isadded to prepare the polyvinyl acetate a). On completion of the meteredaddition of vinyl acetate and of the metered addition of initiator, itis optionally possible to continue polymerization. Subsequently, thesolvent and residual monomer fractions are removed by distillation, andthe product is isolated as solid after the melt has been cooled.

In a further preferred embodiment, the compositions are likewiseproduced by means of solution polymerization, in which case vinylacetate is polymerized in the presence of the vinyl acetate-vinyllaurate copolymer. To this end, the vinyl acetate-vinyl lauratecopolymer is initially charged together with vinyl acetate monomer, andthe polymerization is carried out at a temperature of from 40° C. to120° C. The initiator can be initially charged completely or partly andthe remainder can be metered in. The solvent can be initially chargedcompletely or partly and the remainder can be metered in. Suitablesolvents are aldehydes, ketones, preferably alkanols such as methanol,ethanol, propanol, and isopropanol. On completion of the meteredadditions, it is optionally possible to continue polymerization.Subsequently, the solvent and residual monomer fractions are removed bydistillation, and the product is isolated as a solid after the melt hasbeen cooled.

The melt obtained in the solution polymerization is worked up and thecompounds are obtained as solids analogously to the processes describedfor the production of the compounds by means of mixing of components a)and b), for example by mechanical comminution after cooling the melt,for example in a mill or a crusher, or application of the melt to acooling belt and cooling in the form of strips, slabs or drops. Afurther alternative consists in processing the melt to pellets by meansof underwater granulation, in which case a particle size of from 1 mm to20 mm is preferred and a particle size of from 3 mm to 10 mm isparticularly preferred for the pellets. Solid compositions are thusobtainable in particulate, dosable and free-flowing form.

Irrespective of the production, solid clear particles are obtained, inwhich components a) and b) are distributed homogeneously.

The compositions are suitable especially for the production of chewinggum base. The compositions are preferably used in a proportion of from10 to 60% by weight based on the total weight of the chewing gum base.In addition to the compositions, these materials generally also compriseelastomer, filler and optionally further additives.

Suitable elastomers for chewing gum base are polyisobutylenes,isobutylene-isoprene copolymers, styrene-butadiene copolymers andnatural rubber. The elastomer content is generally from 10 to 50% byweight based on the total weight of the chewing gum base. The elastomercontent is preferably replaced completely or partly by the inventivecomposition composed of polyvinyl acetate and vinyl acetate-vinyllaurate copolymer.

Suitable fillers are magnesium carbonate, calcium carbonate, magnesiumsilicates, aluminum silicates, talc, titanium dioxide, calcium phosphateand cellulose ethers. The filler content in the formulation is generallyfrom 10 to 40% by weight, based on the total weight of the chewing gumbase.

Further additives are waxes such as paraffin wax or polyethylene wax,plasticizers such as rosins or terpene resins, hardened fats or glyceryltriacetate, emulsifiers such as glyceryl monostearate or lecithin,antioxidants, flavorings and colorings. The use amounts of theseadditives are known to those skilled in the art.

It should be pointed out that the amounts of the constituents of thechewing gum base stated in % by weight total to 100% by weight in theformulation.

Chewing gum base is produced by the processes customary for thispurpose. In general, the constituents of the chewing gum base, ifappropriate after a preceding granulation or pulverization step, aremixed, then the mixture is heated to typically from 70° C. to 150° C.,generally to give a melt, and then the chewing gum base is extruded orcast into shape.

EXAMPLE 1

A stirred tank is initially charged with 2 kg of isopropanol togetherwith 16 kg of vinyl acetate, 10 kg of vinyl laurate and 7 g of t-butylperoxo-2-ethylhexanoate, and the polymerization is started by means ofheating of the initial charge to 72° C. At the start, 7 g of t-butylperoxo-2-ethylhexanoate are added and, during the polymerization, 180 gof butyl peroxo-2-ethylhexanoate in 700 g of isopropanol are metered in.240 minutes after the start, the metered addition of 44 kg of vinylacetate was commenced and the metered addition was continued over aperiod of 165 minutes. On completion of metered addition 1, stirring wascontinued for another 25 minutes, the temperature was increased to 120°C., the tank was evacuated, and solvent and residual monomer weredistilled off. The melt was discharged and cooled on a cooling belt togive drop-shaped particles with a size of from 3 to 6 mm. A clearproduct was obtained with two glass transition temperatures Tg₁=2° C.and Tg₂=29° C., and a molecular weight Mw of 141,000.

EXAMPLE 2

A stirred tank was initially charged with 6 kg of isopropanol and 2 kgof vinyl acetate together with 29 kg of a vinyl acetate-vinyl lauratecopolymer (60% by weight of vinyl acetate and 40% by weight of vinyllaurate, Mw=420,000), and the initial charge was heated to 72° C. Thepolymerization was started by means of addition of 14 g of t-butylperoxopivalate. After 20 minutes, the metered addition of 100 g oft-butyl peroxo-2-ethylhexanoate in 272 g of isopropanol was started andwas continued over a period of 3 hours. 50 minutes after the start ofthe reaction, the metered addition of 41 kg of vinyl acetate wascommenced and was continued over 2.5 hours. On completion of the meteredadditions, stirring was continued for another 25 minutes, thetemperature was increased to 120° C., the tank was evacuated, andsolvent and residual monomer were distilled off. The melt was dischargedand processed by means of underwater granulation to give granules with aparticle size of from 1 to 2 mm. A clear product was obtained with twoglass transition temperatures Tg₁=−1° C. and Tg₂=32° C., and a molecularweight Mw of 169,000.

EXAMPLE 3

A laboratory kneader (double-Z kneading hook) was initially charged atfrom 120° C. to 140° C. with 40 parts by weight of a vinyl acetate/vinyllaurate copolymer (60% by weight of vinyl acetate, to which 40% byweight of vinyl laurate, Mw=420,000), and 60 parts by weight of a vinylacetate homopolymer (Mw=15,000) were added, and the mixture was kneadedfor 1 hour to give a composition. Subsequently, the melt was allowed tosolidify to a slab, which was comminuted mechanically to particles witha particle size of from 1 to 20 mm. A clear product was obtained withtwo glass transition temperatures Tg₁=0° C. and Tg₂=38° C.

EXAMPLE 4

A laboratory kneader (double-Z kneading hook) was initially charged atfrom 120° C. to 140° C. with 30 parts by weight of a vinyl acetate/vinyllaurate copolymer (60% by weight of vinyl acetate, 40% by weight ofvinyl laurate, Mw=420,000), and 70 parts by weight of a vinyl acetatehomopolymer (Mw=40,000) were added and the mixture was kneaded for 1hour to give a composition. Subsequently, the melt was allowed tosolidify to a slab, which was comminuted mechanically to particles witha particle size of from 1 to 20 mm. A clear product was obtained withtwo glass transition temperatures Tg₁=0° C. and Tg₂=38° C.

EXAMPLE 5 Production of a Chewing Gum Base

In a conventional kneader, the following ingredients were processed at120° C. to give a gum base:

40 parts by weight of the composition of Example 3

20 parts by weight of glyceryl ester of a partially hydrogenated rosin

20 parts by weight of calcium carbonate

10 parts by weight of microcrystalline wax

5 parts by weight of vegetable fat

3.5 parts by weight of glyceryl monostearate

0.5 part by weight of soya lecithin

The mixing time in order to obtain a homogeneous material was 90minutes.

EXAMPLE 6 Production of a Chewing Gum Base

35 parts by weight of the composition of Example 2

5 parts by weight of polyvinyl acetate (Mw=15,000)

22 parts by weight of glyceryl ester of a partially hydrogenated rosin

25 parts by weight of talc

4 parts by weight of paraffin wax p ≡parts by weight of hydrogenatedrapeseed oil

4 parts by weight of glyceryl monostearate

The mixing time in order to obtain a homogeneous material was 90minutes.

COMPARATIVE EXAMPLE 7 Production of the Chewing Gum Base in ConventionalFormulation

4 parts by weight of butyl rubber

7 parts by weight of polyisobutylene

26 parts by weight of polyvinyl acetate (Mw=15,000)

21 parts by weight of glyceryl ester of a partially hydrogenated rosin

24 parts by weight of talc

8 parts by weight of microcrystalline wax

6 parts by weight of hydrogenated rapeseed oil

4 parts by weight of glyceryl monostearate

The mixing time in order to obtain a homogeneous material was 150minutes.

The comparison of Examples 5 and 6 with comparative Example 7 is thatexchange of the elastomer component and of the polymer resin componentfor the inventive composition significantly reduces the production timeof a chewing gum base. Furthermore, the inventive compositions aresignificantly easier to process compared to conventional vinylacetate-vinyl laurate elastomers, since they are present inready-to-use, particulate form.

EXAMPLE 8 Production of a Sugar-Free Chewing Gum

In a laboratory kneader, a chewing gum mixture was produced at from 45°C. to 60° C. with the following ingredients:

25 parts by weight of chewing gum base from Example 5

15 parts by weight of xylitol

52 parts by weight of sorbitol

6.8 parts by weight of sorbitol syrup

1 part by weight of peppermint oil

0.2 part by weight of aspartame

1. In a chewing gum comprising a chewing gum base composition andfurther additives, the improvement comprising incorporating, as at leastpart of the chewing gum base composition, a homogenous solid elastomercomprising: a) from 50 to 90 percent by weight of a polyvinyl acetatepolymer, and b) from 10 to 50 percent by weight of a vinyl acetate-vinyllaurate copolymer, wherein the percents by weight are based on the totalweight of the homogenous solid elastomer.
 2. The chewing gum of claim 1,wherein the chewing gum base composition comprises from 10 to 60 weightpercent of the homogenous solid elastomer, based on the weight of thechewing gum base composition.
 3. The chewing gum of claim 1, wherein thechewing gum base composition consists of the homogenous solid elastomer.4. The chewing gum of claim 11, wherein the vinyl acetate-vinyl lauratecopolymer contains 60-80 weight percent of vinyl acetate-derivedmoieties and 20-40 weight percent of vinyl laurate-derived moietiesbased on the weight of the vinyl acetate-vinyl laurate copolymer.
 5. Thechewing gum of claim 11, wherein the homogenous solid elastomer isprepared by a process comprising solution polymerizing comonomersincluding vinyl acetate and vinyl laurate to form a vinyl acetate-vinyllaurate copolymer b), following which vinyl acetate monomer is added andpolymerized after a monomer conversion of from 60 to 100% by weight ofthe comonomers used to form copolymer b), and isolating the product as asolid, wherein the homogenous solid elastomer comprises from 50-90% byweight, based on the total weight of the homogenous solid elastomer, ofa) a polyvinyl acetate polymer containing more than 90% by weight ofvinyl acetate derived moieties based on the weight of the polyvinylacetate polymer, and from 10 to 50% by weight based on the total weightof the homogenous solid elastomer, of b) a vinyl acetate-vinyl lauratecopolymer containing 10-50% of vinyl laurate derived moieties based onthe weight of the vinyl acetate-vinyl laurate copolymer.
 6. The chewinggum of claim 1, wherein the vinyl acetate polymer contains less than 10weight percent of vinyl laurate-derived moieties, based on the weight ofthe vinyl acetate polymer.
 7. The chewing gum of claim 1, wherein thevinyl acetate polymer contains less than 5 weight percent of vinyllaurate-derived moieties, based on the weight of the vinyl acetatepolymer.
 8. The chewing gum of claim 1, wherein the homogenous solidelastomer is prepared by separately preparing a vinyl acetate polymerand a vinyl acetate-vinyl laurate copolymer, and blending the vinylacetate polymer and the vinyl acetate-vinyl laurate copolymer in themelt, and solidifying the melt.
 9. The chewing gum of claim 1, whereinthe homogenous solid elastomer is prepared by dissolving a vinylacetate-vinyl laurate copolymer in solvent, adding vinyl acetatemonomer, polymerizing the vinyl acetate monomer, and removing solvent toform a homogenous solid elastomer.
 10. The chewing gum of claim 1,wherein the homogenous solid elastomer comprises from 65 to 75 weightpercent vinyl acetate polymer and 35 to 25 weight percent vinylacetate-vinyl laurate copolymer, based on the weight of the homogenoussolid elastomer.
 11. The chewing gum of claim 1, wherein theweight-average molecular weight Mw of the polyvinyl acetate polymer a)is from 10,000 to 100,000 and the weight-average molecular weight Mw ofthe vinyl acetate-vinyl laurate copolymer b) is from 100,000 to 600,000.